1. Field of the Invention
The present invention relates to a surface-emitting-type semiconductor laser device having a buried structure.
2. Description of Related Art
Generally, the surface-emitting-type semiconductor laser device having a buried structure has a configuration wherein a buried part having a double heterostructure consisting of a cladding layer, an active layer, a cladding layer and a cap layer and a burying part which is located around this buried part and has a current blocking function are formed on a semiconductor substrate. Then, it provides a dielectric multilayer film, for example, a TiO.sub.2 /SiO.sub.2 film as a reflecting mirror on the surface of the buried part.
Then, in such a laser device, since the reflecting mirror is formed by a dielectric multilayer film, the heat conductivity is poor, and the heat discharge from the buried part to a heat sink installed in contact with the dielectric multilayer film is insufficient. Also, the size of the reflecting mirror itself is limited due to the arrangement of current injection to the buried part, and a reduction in the reflecting area is inevitable. Furthermore, there has been the problem that since the reflecting mirror is not electrically conductive, an electrode has to be formed at a position separate from the reflecting mirror, and the manufacturing process is complicated, and the efficiency of current injection is poor.
Then, a surface-emitting-type semiconductor laser device has been developed which uses a semiconductor multilayer film electrically conductive as a reflecting mirror. Such a laser device has advantages as described below. Since the semiconductor multilayer film excels in heat conductivity, the efficiency of heat discharge from the buried part to the heat sink is high. Also, since the semiconductor multilayer film is electrically conductive, it can have an additional function as a carrier injecting part into the buried part, and the efficiency of current injection is improved. Furthermore, since the semiconductor multilayer film is electrically conductive, the size of the reflecting mirror can be set arbitrarily, and a sufficient reflecting area can be obtained.
However, the design of the semiconductor multilayer film constituting the reflecting mirror has not been investigated sufficiently, and the surface-emitting-type semiconductor laser device wherein the reflecting mirror is constituted with the semiconductor multilayer film cannot make a stable laser oscillation yet.